tdw wrote:

It is - a circular housing (approx 50mm diameter) in which is a tiny light
globe (I can't read the wattage but by the look of it no more than one watt)
which is connected to a three - four metre long cable with a two pin plug
(for a 12v outlet) on the end. The housing itself is then enclosed by a
removeable piece of red glass. I suppose it could be intended for use as a
cockpit light that won't harm night vision but the output seems far too low
for it be effective although the length of cable is about right to cover the
distance from power outlets at the nav station to the instrument binnacle in
the cockpit.

Sounds like a cockpit light that won't harm night vision to me. Have you
actually tried it at night to see how much light it emits? If you're
using your night vision then it's not going to have to produce very much
light to be useful. Even if it doesn't flood the cockpit with red light,
it could probably illuminate a chart held next to it, and that might be
all you need.

Pete